The disposal of plastic wastes is connected with great difficulties because, on the one hand, their combustion, due to the relatively high halogen content of the customarily employed plastics, produces aggressive combustion products which lead to great damage to the environment and, on the other hand, when stored in waste dumps, they either do not decompose at all or toxic byproducts are formed.
In view of these difficulties, it has been desired for some time to develop biodegradable plastic materials which are easily decomposed in waste dumps and do not produce environmentally damaging fission products so that their disposal does not pose difficulties while, on the other hand, their technical characteristics are such that they fully meet all expected requirements placed on them with respect to their being processed into plastic articles and with a view toward the characteristics of the plastic articles.
Cellulose esters, such as, for example, cellulose acetate and cellulose acetobutyrate, due to their low cost, have caught the attention of plastic processors for some time. Cellulose acetobutyrate includes approximately 20% acetate groups and 40% butyrate groups.
U.S. Pat. Nos. 4,729,793 and 4,731,122, for example, disclose transparent plastic objects made of cellulose acetate and cellulose acetobutyrate which contain, in addition to polyethylene glycol as softener, tributyl citrate and triethyl citrate. The cited patents do not disclose anything regarding biodegradability of these plastic objects.
Based on this state of the art, it is now the object of the present invention to create novel biodegradable and moldable plastic materials based on cellulose esters and carboxylic acid esters which are transparent or at least translucent and exhibit, on the one hand, the characteristics required for the manufacture of plastic objects by conventional means such as injection molding, blow molding, etc., which when shaped into such objects, have a sufficiently long service life and, on the other hand, are biodegradable after use in a sufficiently short period of time without creating damaging or harmful degradation reaction products.